Aqueous dispersions of polymer-enclosed particles, related coating compositions and coated substrates

ABSTRACT

Disclosed are aqueous dispersions of polymer-enclosed particles, such as nanoparticles. Also disclosed are methods for making an aqueous dispersion of polymer-enclosed particles, polymerizable polymers useful in such a method, powder coating compositions formed from such an aqueous dispersion, substrates at least partially coated with such a composition, and reflective surfaces comprising a non-hiding coating layer deposited from such a composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/337,062, filed Jan. 20, 2006, which is entitled “AqueousDispersions of Polymer-Enclosed Particles, Related Coating Compositionsand Coated Substrates”, which is a continuation-in-part of: (i) U.S.patent application Ser. No. 10/876,031, entitled, “Aqueous Dispersionsof Microparticles Having a Nanoparticulate Phase and CoatingCompositions Containing The Same”; (ii) U.S. patent application Ser. No.10/809,764, which was filed on Mar. 25, 2004, and is entitled, “ProcessFor Manufacturing Powder Coating Compositions Introducing Hard toIncorporate Additives and/or Providing Dynamic Color Control; (iii) U.S.patent application Ser. No. 10/809,595, which was filed on Mar. 25,2004, and is entitled, “Focused Heat Extrusion Process For ManufacturingPowder Coating Compositions”; and (iv) U.S. patent application Ser. No.10/809,639, which was filed on Mar. 25, 2004, and is entitled,“Apparatus For Manufacturing Thermosetting Powder Coating CompositionsWith Dynamic Control Including Low Pressure Injection Systems”, each ofwhich being incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to, among other things, aqueousdispersions of polymer-enclosed particles, such as nanoparticles,methods for making such an aqueous dispersion, polymerizable polymersuseful in such a method, powder coating compositions formed from such anaqueous dispersion, and substrates at least partially coated with such acomposition.

BACKGROUND INFORMATION

Coating compositions, such as powder coating compositions, often includecolorant and/or filler particles to impart color and/or performanceproperties in the resulting coating. Pigment particles tend to have astrong affinity for each other and, unless separated, tend to clumptogether to form agglomerates. Therefore, these agglomerates are oftendispersed in a resinous grind vehicle and, optionally, dispersants bymilling or grinding using high shear techniques to break up theagglomerates. If nano-sized pigment particles are desired, furthermilling is often required to obtain the desired particle size.

Pigments and fillers usually consist of solid crystalline particlesranging in diameter from about 0.02 to 2 microns (i.e., 20 to 2000nanometers). Agglomeration is a serious problem for nano-sized particlepigments and filler materials (such as carbon black) in particularbecause these nanoparticles have a relatively large surface area. Thus,acceptable dispersion of such nanoparticles often requires an inordinateamount of resinous grind vehicle and/or dispersant to effectde-agglomeration and to prevent subsequent re-agglomeration of thenanoparticles.

The presence of such high levels of resinous grind vehicles anddispersants, however, in the final coating composition can bedetrimental to the resultant coating. For example, high levels ofdispersants have been known to contribute to water sensitivity of theresultant coating. Also, some resinous grind vehicles, for example,acrylic grind vehicles, can negatively impact coating performanceproperties such as chip resistance and flexibility.

Powder coatings compositions for use in coating various types ofsubstrates are often desired. Such coating compositions can greatlyreduce, or even eliminate, the use of organic solvents that are oftenused in liquid coating compositions. When a powder coating compositionis cured by heating, little if any volatile material is given off to thesurrounding environment. This is a significant advantage over liquidcoating compositions in which organic solvent is volatized into thesurrounding atmosphere when the coating composition is cured by heating.

It would also be desirable to provide an aqueous dispersion ofresin-enclosed particles, wherein re-agglomeration of the particles isminimized, and which may be suitable for use in preparing powder coatingcompositions.

SUMMARY OF THE INVENTION

In certain respects, the present invention is directed to aqueousdispersions comprising polymer-enclosed particles, wherein thepolymer-enclosed particles comprise particles enclosed by a friablepolymer. The present invention is also directed to powder coatingcompositions comprising such polymer-enclosed particles, substrates atleast partially coated with such powder coating compositions, andsubstrates at least partially coated with a multi-layer compositecoating wherein at least one coating layer is deposited from such apowder coating composition.

In other respects, the present invention is directed to methods formaking an aqueous dispersion of polymer-enclosed particles. The methodscomprise (1) providing a mixture, in an aqueous medium, of (a)particles, (b) a polymerizable ethylenically unsaturated monomer, and(c) a water-dispersible polymerizable dispersant, and (2) polymerizingthe ethylenically unsaturated monomer and polymerizable dispersant toform polymer-enclosed particles comprising a water-dispersible polymer.

In other respects, the present invention is directed to methods formaking polymer-enclosed particles. The methods comprise (1) providing amixture, in an aqueous medium, of (a) particles, (b) a polymerizableethylenically unsaturated monomer, and (c) a water-dispersiblepolymerizable dispersant; (2) polymerizing the ethylenically unsaturatedmonomer and polymerizable dispersant to form an aqueous dispersioncomprising polymer-enclosed particles comprising a water-dispersible,friable polymer; (3) removing water from the aqueous dispersion to forma solid material comprising the polymer-enclosed particles, and (4)fragmenting the solid material.

In other respects, the present invention is directed to methods formaking powder coating compositions comprising (1) introducing to anextruder (a) an aqueous dispersion of polymer-enclosed particles, and(b) dry materials; (2) blending (a) and (b) in the extruder; (3)devolatilizing the blend to form an extrudate; (3) cooling theextrudate, and (4) milling the extrudate to a desired particle size.

In still other respects, the present invention is directed to methodsfor increasing the chromaticity of a powder coating composition. Thesemethods comprise including in the powder coating composition a pluralityof polymer-enclosed nanoparticles having a maximum haze of 10%.

In yet other respects, the present invention is directed to methods formatching the color of a preselected protective and decorative coatingdeposited from a liquid coating composition. These methods comprise: (a)determining the visible color of the preselected coating by measuringthe absorbance or reflectance of the preselected coating; and (b) makinga powder coating composition comprising a plurality of polymer-enclosednanoparticles having a maximum haze of 10%, wherein a coating depositedfrom the powder coating composition matches the visible color of thepreselected coating.

The present invention is also directed to water-dispersible,polymerizable polyester polyurethanes comprising terminal ethylenicallyunsaturated groups. The polyurethanes are prepared from reactantscomprising (a) a polyisocyanate, (b) a polyester polyol, (c) apolyamine, (d) a material having an ethylenically unsaturated group andan active hydrogen group, and (e) a material having an acid functionalgroup or anhydride and an active hydrogen group.

In addition, the present invention is directed to reflective surfaces atleast partially coated with a transparent tinted coating exhibiting aplurality of hues, wherein the transparent tinted coating is depositedfrom a coating composition comprising polymer-enclosed color-impartingparticles, wherein the coating has a plurality of thicknesses.

Also, the present invention is directed to reflective surfaces at leastpartially coated with a multi-layer composite coating. These multi-layercomposite coatings comprise: (a) a first transparent tinted coatingexhibiting a first color; and (b) a second transparent tinted coatingdeposited over at least a portion of the first transparent tintedcoating and exhibiting a second color different from the first color.Moreover, the first transparent tinted coating and the secondtransparent tinted coating are deposited from a coating compositioncomprising polymer-enclosed color-imparting particles, and at least oneof the transparent tinted coatings have a plurality of thicknesses.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

As previously mentioned, certain embodiments of the present inventionare directed to aqueous dispersions of polymer-enclosed particles. Asused herein, the term “dispersion” refers to a two-phase system in whichone phase includes finely divided particles distributed throughout asecond phase, which is a continuous phase. The dispersions of thepresent invention often are oil-in-water emulsions, wherein an aqueousmedium provides the continuous phase of the dispersion in which thepolymer-enclosed particles are suspended as the organic phase.

As used herein, the term “aqueous”, “aqueous phase”, “aqueous medium,”and the like, refers to a medium that either consists exclusively ofwater or comprises predominantly water in combination with anothermaterial, such as, for example, an inert organic solvent. In certainembodiments, the amount of organic solvent present in the aqueousdispersions of the present invention is less than 20 weight percent,such as less than 10 weight percent, or, in some cases, less than 5weight percent, or, in yet other cases, less than 2 weight percent, withthe weight percents being based on the total weight of the dispersion.Non-limiting examples of suitable organic solvents are propylene glycolmonobutyl ether, ethylene glycol monohexyl ether, ethylene glycolmonobutyl ether, n-butanol, benzyl alcohol, and mineral spirits.

As used herein, the term “polymer-enclosed particles” refers toparticles that are at least partially enclosed by, i.e., confinedwithin, a polymer to an extent sufficient to physically separateparticles from each other within the aqueous dispersion, therebypreventing significant agglomeration of the particles. It will beappreciated, of course, that the dispersions of the present inventionmay also include particles that are not polymer-enclosed particles.

In certain embodiments, the particles that are enclosed by a polymer inthe aqueous dispersions of the present invention comprise nanoparticles.As used herein, the term “nanoparticles” refers to particles that havean average particle size of less than 1 micron. In certain embodiments,the nanoparticles used in the present invention have an averageparticles size of 300 nanometers or less, such as 200 nanometers orless, or, in some cases, 100 nanometers or less. Therefore, in certainembodiments, the aqueous dispersions of the present invention comprisenanoparticles that are polymer-enclosed and, therefore, are notsignificantly agglomerated.

For purposes of the present invention, average particle size can bemeasured according to known laser scattering techniques. For example,average particle size can be determined using a Horiba Model LA 900laser diffraction particle size instrument, which uses a helium-neonlaser with a wave length of 633 nm to measure the size of the particlesand assumes the particle has a spherical shape, i.e., the “particlesize” refers to the smallest sphere that will completely enclose theparticle. Average particle size can also be determined by visuallyexamining an electron micrograph of a transmission electron microscopy(“TEM”) image of a representative sample of the particles, measuring thediameter of the particles in the image, and calculating the averageprimary particle size of the measured particles based on magnificationof the TEM image. One of ordinary skill in the art will understand howto prepare such a TEM image and determine the primary particle sizebased on the magnification. The primary particle size of a particlerefers to the smallest diameter sphere that will completely enclose theparticle. As used herein, the term “primary particle size” refers to thesize of an individual particle.

The shape (or morphology) of the particles can vary. For example,generally spherical morphologies (such as solid beads, microbeads, orhollow spheres), can be used, as well as particles that are cubic,platy, or acicular (elongated or fibrous). Additionally, the particlescan have an internal structure that is hollow, porous or void free, or acombination of any of the foregoing, e.g., a hollow center with porousor solid walls. For more information on suitable particlecharacteristics see H. Katz et al. (Ed.), Handbook of Fillers andPlastics (1987) at pages 9-10.

Depending on the desired properties and characteristics of the resultantdispersion and/or coating compositions of the present invention (e.g.,coating hardness, scratch resistance, stability, or color), mixtures ofone or more particles having different average particle sizes can beemployed.

The particles, such as nanoparticles, present in the aqueous dispersionsof the present invention can be formed from polymeric and/ornon-polymeric inorganic materials, polymeric and/or non-polymericorganic materials, composite materials, as well as mixtures of any ofthe foregoing. As used herein, “formed from” denotes open, e.g.,“comprising,” claim language. As such, it is intended that a compositionor substance “formed from” a list of recited components be a compositioncomprising at least these recited components, and can further compriseother, non-recited components, during the composition's formation.Additionally, as used herein, the term “polymer” is meant to encompassoligomers, and includes without limitation both homopolymers andcopolymers.

As used herein, the term “polymeric inorganic material” means apolymeric material having a backbone repeat unit based on an element orelements other than carbon. Moreover, as used herein, the term“polymeric organic materials” means synthetic polymeric materials,semi-synthetic polymeric materials and natural polymeric materials, allof which have a backbone repeat unit based on carbon.

The term “organic material,” as used herein, means carbon containingcompounds wherein the carbon is typically bonded to itself and tohydrogen, and often to other elements as well, and excludes binarycompounds such as the carbon oxides, the carbides, carbon disulfide,etc.; such ternary compounds as the metallic cyanides, metalliccarbonyls, phosgene, carbonyl sulfide, etc.; and carbon-containing ioniccompounds such as metallic carbonates, for example calcium carbonate andsodium carbonate.

As used herein, the term “inorganic material” means any material that isnot an organic material.

As used herein, the term “composite material” means a combination of twoor more differing materials. The particles formed from compositematerials generally have a hardness at their surface that is differentfrom the hardness of the internal portions of the particle beneath itssurface. More specifically, the surface of the particle can be modifiedin any manner well known in the art, including, but not limited to,chemically or physically changing its surface characteristics usingtechniques known in the art.

For example, a particle can be formed from a primary material that iscoated, clad or encapsulated with one or more secondary materials toform a composite particle that has a softer surface. In certainembodiments, particles formed from composite materials can be formedfrom a primary material that is coated, clad or encapsulated with adifferent form of the primary material. For more information onparticles useful in the present invention, see G. Wypych, Handbook ofFillers, 2nd Ed. (1999) at pages 15-202.

As aforementioned, the particles useful in the present invention caninclude any inorganic materials known in the art. Suitable particles canbe formed from ceramic materials, metallic materials, and mixtures ofany of the foregoing. Non-limiting examples of such ceramic materialscan comprise metal oxides, mixed metal oxides, metal nitrides, metalcarbides, metal sulfides, metal silicates, metal borides, metalcarbonates, and mixtures of any of the foregoing. A specific,non-limiting example of a metal nitride is boron nitride; a specific,non-limiting example of a metal oxide is zinc oxide; non-limitingexamples of suitable mixed metal oxides are aluminum silicates andmagnesium silicates; non-limiting examples of suitable metal sulfidesare molybdenum disulfide, tantalum disulfide, tungsten disulfide, andzinc sulfide; non-limiting examples of metal silicates are aluminumsilicates and magnesium silicates, such as vermiculite.

In certain embodiments of the present invention, the particles compriseinorganic materials selected from aluminum, barium, bismuth, boron,cadmium, calcium, cerium, cobalt, copper, iron, lanthanum, magnesium,manganese, molybdenum, nitrogen, oxygen, phosphorus, selenium, silicon,silver, sulfur, tin, titanium, tungsten, vanadium, yttrium, zinc, andzirconium, including oxides thereof, nitrides thereof, phosphidesthereof, phosphates thereof, selenides thereof, sulfides thereof,sulfates thereof, and mixtures thereof. Suitable non-limiting examplesof the foregoing inorganic particles include alumina, silica, titania,ceria, zirconia, bismuth oxide, magnesium oxide, iron oxide, aluminumsilicate, boron carbide, nitrogen doped titania, and cadmium selenide.

The particles can comprise, for example, a core of essentially a singleinorganic oxide, such as silica in colloidal, fumed, or amorphous form,alumina or colloidal alumina, titanium dioxide, iron oxide, cesiumoxide, yttrium oxide, colloidal yttria, zirconia, e.g., colloidal oramorphous zirconia, and mixtures of any of the foregoing; or aninorganic oxide of one type upon which is deposited an organic oxide ofanother type.

Non-polymeric, inorganic materials useful in forming the particles usedin the present invention can comprise inorganic materials selected fromgraphite, metals, oxides, carbides, nitrides, borides, sulfides,silicates, carbonates, sulfates, and hydroxides. A non-limiting exampleof a useful inorganic oxide is zinc oxide. Non-limiting examples ofsuitable inorganic sulfides include molybdenum disulfide, tantalumdisulfide, tungsten disulfide, and zinc sulfide. Non-limiting examplesof useful inorganic silicates include aluminum silicates and magnesiumsilicates, such as vermiculite. Non-limiting examples of suitable metalsinclude molybdenum, platinum, palladium, nickel, aluminum, copper, gold,iron, silver, alloys, and mixtures of any of the foregoing.

In certain embodiments, the particles can be selected from fumed silica,amorphous silica, colloidal silica, alumina, colloidal alumina, titaniumdioxide, iron oxide, cesium oxide, yttrium oxide, colloidal yttria,zirconia, colloidal zirconia, and mixtures of any of the foregoing. Incertain embodiments, the particles comprise colloidal silica. Asdisclosed above, these materials can be surface treated or untreated.Other useful particles include surface-modified silicas, such as aredescribed in U.S. Pat. No. 5,853,809 at column 6, line 51 to column 8,line 43, incorporated herein by reference.

As another alternative, a particle can be formed from a primary materialthat is coated, clad or encapsulated with one or more secondarymaterials to form a composite material that has a harder surface.Alternatively, a particle can be formed from a primary material that iscoated, clad or encapsulated with a differing form of the primarymaterial to form a composite material that has a harder surface.

In one example, and without limiting the present invention, an inorganicparticle formed from an inorganic material, such as silicon carbide oraluminum nitride, can be provided with a silica, carbonate or nanoclaycoating to form a useful composite particle. In another non-limitingexample, a silane coupling agent with alkyl side chains can interactwith the surface of an inorganic particle formed from an inorganic oxideto provide a useful composite particle having a “softer” surface. Otherexamples include cladding, encapsulating or coating particles formedfrom non-polymeric or polymeric materials with differing non-polymericor polymeric materials. A specific non-limiting example of suchcomposite particles is DUALITE™, which is a synthetic polymeric particlecoated with calcium carbonate that is commercially available from Pierceand Stevens Corporation of Buffalo, N.Y.

In certain embodiments, the particles used in the present invention havea lamellar structure. Particles having a lamellar structure are composedof sheets or plates of atoms in hexagonal array, with strong bondingwithin the sheet and weak van der Waals bonding between sheets,providing low shear strength between sheets. A non-limiting example of alamellar structure is a hexagonal crystal structure. Inorganic solidparticles having a lamellar fullerene (i.e., buckyball) structure arealso useful in the present invention.

Non-limiting examples of suitable materials having a lamellar structureinclude boron nitride, graphite, metal dichalcogenides, mica, talc,gypsum, kaolinite, calcite, cadmium iodide, silver sulfide and mixturesthereof. Suitable metal dichalcogenides include molybdenum disulfide,molybdenum diselenide, tantalum disulfide, tantalum diselenide, tungstendisulfide, tungsten diselenide and mixtures thereof.

The particles can be formed from non-polymeric, organic materials.Non-limiting examples of non-polymeric, organic materials useful in thepresent invention include, but are not limited to, stearates (such aszinc stearate and aluminum stearate), diamond, carbon black andstearamide.

The particles used in the present invention can be formed from inorganicpolymeric materials. Non-limiting examples of useful inorganic polymericmaterials include polyphosphazenes, polysilanes, polysiloxanes,polygermanes, polymeric sulfur, polymeric selenium, silicones andmixtures of any of the foregoing. A specific, non-limiting example of aparticle formed from an inorganic polymeric material suitable for use inthe present invention is Tospearl, which is a particle formed fromcross-linked siloxanes and is commercially available from ToshibaSilicones Company, Ltd. of Japan.

The particles can be formed from synthetic, organic polymeric materials.Non-limiting examples of suitable organic polymeric materials include,but are not limited to, thermoset materials and thermoplastic materials.Non-limiting examples of suitable thermoplastic materials includethermoplastic polyesters, such as polyethylene terephthalate,polybutylene terephthalate and polyethylene naphthalate, polycarbonates,polyolefins, such as polyethylene, polypropylene and polyisobutene,acrylic polymers, such as copolymers of styrene and an acrylic acidmonomer and polymers containing methacrylate, polyamides, thermoplasticpolyurethanes, vinyl polymers, and mixtures of any of the foregoing.

Non-limiting examples of suitable thermoset materials include thermosetpolyesters, vinyl esters, epoxy materials, phenolics, aminoplasts,thermoset polyurethanes and mixtures of any of the foregoing. Aspecific, non-limiting example of a synthetic polymeric particle formedfrom an epoxy material is an epoxy microgel particle.

The particles can also be hollow particles formed from materialsselected from polymeric and non-polymeric inorganic materials, polymericand non-polymeric organic materials, composite materials and mixtures ofany of the foregoing. Non-limiting examples of suitable materials fromwhich the hollow particles can be formed are described above.

In certain embodiments, the particles used in the present inventioncomprise an organic pigment, for example, azo compounds (monoazo,di-azo, β-Naphthol, Naphthol AS salt type azo pigment lakes,benzimidazolone, di-azo condensation, isoindolinone, isoindoline), andpolycyclic (phthalocyanine, quinacridone, perylene, perinone,diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone,anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine,triarylcarbonium, quinophthalone) pigments, and mixtures of any of theforegoing. In certain embodiments, the organic material is selected fromperylenes, quinacridones, phthalocyanines, isoindolines, dioxazines(that is, triphenedioxazines), 1,4-diketopyrrolopyrroles,anthrapyrimidines, anthanthrones, flavanthrones, indanthrones,perinones, pyranthrones, thioindigos,4,4′-diamino-1,1′-dianthraquinonyl, as well as substituted derivativesthereof, and mixtures thereof.

Perylene pigments used in the practice of the present invention may beunsubstituted or substituted. Substituted perylenes may be substitutedat imide nitrogen atoms for example, and substituents may include analkyl group of 1 to 10 carbon atoms, an alkoxy group of 1 to 10 carbonatoms and a halogen (such as chlorine) or combinations thereof.Substituted perylenes may contain more than one of any one substituent.The diimides and dianhydrides of perylene-3,4,9,10-tetracarboxylic acidare preferred. Crude perylenes can be prepared by methods known in theart.

Phthalocyanine pigments, especially metal phthalocyanines may be used.Although copper phthalocyanines are more readily available, othermetal-containing phthalocyanine pigments, such as those based on zinc,cobalt, iron, nickel, and other such metals, may also be used.Metal-free phthalocyanines are also suitable. Phthalocyanine pigmentsmay be unsubstituted or partially substituted, for example, with one ormore alkyl (having 1 to 10 carbon atoms), alkoxy (having 1 to 10 carbonatoms), halogens such as chlorine, or other substituents typical ofphthalocyanine pigments. Phthalocyanines may be prepared by any ofseveral methods known in the art. They are typically prepared by areaction of phthalic anhydride, phthalonitrile, or derivatives thereof,with a metal donor, a nitrogen donor (such as urea or the phthalonitrileitself), and an optional catalyst, preferably in an organic solvent.

Quinacridone pigments, as used herein, include unsubstituted orsubstituted quinacridones (for example, with one or more alkyl, alkoxy,halogens such as chlorine, or other substituents typical of quinacridonepigments), and are suitable for the practice of the present invention.The quinacridone pigments may be prepared by any of several methodsknown in the art but are preferably prepared by thermally ring-closingvarious 2,5-dianilinoterephthalic acid precursors in the presence ofpolyphosphoric acid.

Isoindoline pigments, which can optionally be substituted symmetricallyor unsymmetrically, are also suitable for the practice of the presentinvention can be prepared by methods known in the art. A suitableisoindoline pigment, Pigment Yellow 139, is a symmetrical adduct ofiminoisoindoline and barbituric acid precursors. Dioxazine pigments(that is, triphenedioxazines) are also suitable organic pigments and canbe prepared by methods known in the art.

Mixtures of any of the previously described inorganic particles and/ororganic particles can also be used.

The particles useful in the aqueous dispersions of the present inventioncan comprise color-imparting particles. By the term “color-impartingparticles” is meant a particle that significantly absorbs somewavelengths of visible light, that is, wavelengths ranging from 400 to700 nm, more than it absorbs other wavelengths in the visible region.

If desired, the particles described above can be formed intonanoparticles. In certain embodiments, the nanoparticles are formed insitu during formation of the aqueous dispersion of polymer-enclosedparticles, as described in more detail below. In other embodiments,however, the nanoparticles are formed prior to their incorporation intothe aqueous dispersion. In these embodiments, the nanoparticles can beformed by any of a number of various methods known in the art. Forexample, the nanoparticles can be prepared by pulverizing andclassifying the dry particulate material. For example, bulk pigmentssuch as any of the inorganic or organic pigments discussed above, can bemilled with milling media having a particle size of less than 0.5millimeters (mm), or less than 0.3 mm, or less than 0.1 mm. The pigmentparticles typically are milled to nanoparticle sizes in a high energymill in one or more solvents (either water, organic solvent, or amixture of the two), optionally in the presence of a polymeric grindvehicle. If necessary, a dispersant can be included, for example, (if inorganic solvent) SOLSPERSE® 32000 or 32500 available from LubrizolCorporation, or (if in water) SOLSPERSE® 27000, also available fromLubrizol Corporation. Other suitable methods for producing thenanoparticles include crystallization, precipitation, gas phasecondensation, and chemical attrition (i.e., partial dissolution).

In certain embodiments, the polymer-enclosed color-imparting particlesused in the present invention comprise, for example, a polymer selectedfrom acrylic polymers, polyurethane polymers, polyester polymers,polyether polymers, silicon-based polymers, co-polymers thereof, andmixtures thereof. Such polymers can be produced by any suitable methodknown to those skilled in the art to which the present inventionpertains. Suitable polymer include those disclosed in U.S. patentapplication Ser. No. 10/876,031 at [0061] to [0076], the cited portionof which being incorporated by reference herein, and United StatesPatent Application Publication No. 2005/0287348 A1 at [0042] to [0044],the cited portion of which being incorporation by reference herein.

As indicated, in other embodiments, however, the aqueous dispersions ofthe present invention comprise particles enclosed by a friable polymer.As used herein, the term “friable polymer” refers to a polymer that iseasily pulverized at ambient conditions. That is, upon removal of liquidmaterials from the dispersion, the resulting solid material is easilybroken into small fragments or pieces, such as would be suitable as adry feed material to an extruder to produce a powder coatingcomposition. A film-forming polymer, on the other hand, would, uponremoval of liquid materials from the dispersion, form a self-supportingcontinuous film on at least a horizontal surface of a substrate. As usedherein, the term “ambient conditions” refers to refers to surroundingconditions, which is often around one atmosphere of pressure, 50%relative humidity, and 25° C.

In certain embodiments of the present invention, the friable polymercomprises the reaction product of (i) a polymerizable polyesterpolyurethane, and (ii) an ethylenically unsaturated monomer. As usedherein, the term “polymerizable polyester polyurethane” refers to apolymer that includes a plurality of ester units,

and a plurality of urethane units,

has functional groups that are capable of being polymerized to form alarger polymer, and wherein R¹ is an alkyl, cycloalkyl or oxyalkylmoiety, R² is an alkyl or cycloalkyl moiety, and R³ is alkyl,cycloalkyl, arakyl, or aromatic moiety. In certain embodiments, thepolymerizable polyester polyurethane comprises a polyester polyurethanehaving terminal ethylenic unsaturation. As used herein, the phrase“terminal ethylenic unsaturation” means that at least some of theterminal ends of the polyester polyurethane contain a functional groupcontaining ethylenic unsaturation. Such polyester polyurethanes may alsoinclude, but need not necessarily include, internal ethylenicunsaturation. As a result, in certain embodiments, the aqueousdispersions of the present invention comprise a polymerizable polyesterpolyurethane having terminal ethylenic unsaturation which is preparedfrom reactants comprising (a) a polyisocyanate, (b) a polyester polyol,and (c) a material comprising an ethylenically unsaturated group and anactive hydrogen group. In certain embodiments, the polymerizablepolyester polyurethane utilized in the aqueous dispersions of thepresent invention is formed from reactants further comprising (d) apolyamine, and/or (e) a material comprising an acid functional group oranhydride and a functional group reactive with isocyanate or hydroxylgroups. As used herein, the term “active-hydrogen group” refers tofunctional groups that are reactive with isocyanates as determined bythe Zerewitnoff test as described in the JOURNAL OF THE AMERICANCHEMICAL SOCIETY, Vol. 49, page 3181 (1927).

Polyisocyanates suitable for use in preparing the polymerizablepolyester polyurethane include aliphatical, cycloaliphatical,araliphatical, and/or aromatic isocyanates, and mixtures thereof.

Examples of useful aliphatic and cycloaliphatic polyisocyanates include4,4-methylenebisdicyclohexyl diisocyanate (hydrogenated MDI),hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI),methylenebis(cyclohexyl isocyanate), trimethyl hexamethylenediisocyanate (TMDI), meta-tetramethylxylylene diisocyanate (TMXDI), andcyclohexylene diisocyanate (hydrogenated XDI). Other aliphaticpolyisocyanates include isocyanurates of IPDI and HDI.

Examples of suitable aromatic polyisocyanates include tolylenediisocyanate (TDI) (i.e., 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate or a mixture thereof), diphenylmethane-4,4-diisocyanate(MDI), naphthalene-1,5-diisocyanate (NDI), 3,3-dimethyl-4,4-biphenylenediisocyanate (TODI), crude TDI (i.e., a mixture of TDI and an oligomerthereof), polymethylenepolyphenyl polyisocyanate, crude MDI (i.e., amixture of MDI and an oligomer thereof), xylylene diisocyanate (XDI) andphenylene diisocyanate.

Polyisocyanate derivatives prepared from hexamethylene diisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (“IPDI”),including isocyanurates thereof, and/or4,4′-bis(isocyanatocyclohexyl)methane are suitable.

In certain embodiments, the amount of polyisocyanate used to prepare thepolymerizable polyester polyurethane ranges from 20 to 70 percent byweight, such as 30 to 60 percent by weight or, in some cases, 40 to 50percent by weight, with the weight percents being based on the totalweight of resin solids used to prepare the polymerizable polyesterpolyurethane.

Polyester polyols suitable for use in preparing the polymerizablepolyester polyurethane may be prepared by any suitable methods, e.g.,using saturated dicarboxylic acids or anhydrides thereof (or combinationof acids and anhydrides) and polyhydric alcohols, or by ring opening ofcaprolactones, e.g., epsilon caprolactone. Such polyester polyols arecommercially available in various molecular weights. Aliphaticdicarboxylic acids suitable for preparing polyesters include thosecontaining from 4 to 14, such as 6 to 10, carbon atoms inclusive.Examples of such dicarboxylic acids include: succinic acid, glutaricacid, adipic acid, pimelic acid, suberic acid, azelaic aid and sebacicacid. Corresponding anhydrides can also be used. Typically, adipic andazelaic acids are used.

Polyhydric alcohols used in the preparation of polyester polyolssuitable for use in preparing the polymerizable polyester polyurethaneutilized in certain embodiments of the present invention include,without limitation, aliphatic alcohols containing at least 2 hydroxygroups, e.g., straight chain glycols containing from 2 to 15, such as 4to 8, carbon atoms inclusive. In certain embodiments, the glycolscontain hydroxyl groups in the terminal positions. Non-limiting examplesof such polyhydric alcohols include ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, 1,3-propane diol, 1,3-butanediol, 1,4-butane diol, 1,5-pentane diol, 2,2-dimethylpropane diol,1,5-hexane diol, 1,7-heptane diol, 1,8-octane diol, 1,10-decane diol andmixtures of such polyhydric alcohols.

In certain embodiments, the polyester polyol is prepared by reacting adicarboxylic acid (or anhydride thereof) with a polyhydric alcohol inthe presence of an esterification catalyst, such as an organo tincatalyst. The amount of acid and alcohol used will vary and depend onthe molecular weight polyester desired. Hydroxy terminated polyestersare obtained by utilizing an excess of the alcohol, thereby to obtainlinear chains containing a preponderance of terminal hydroxyl groups.Examples of polyesters include: poly(1,4-butylene adipate),poly(1,4-butylene succinate), poly(1,4-butylene glutarate),poly(1,4-butylene pimelate), poly(1,4-butylene suberate),poly(1,4-butylene azelate), poly(1,4butylene sebacate) and poly(epsiloncaprolactone). In certain embodiments, the polyester polyol utilized inpreparing the friable, polymerizable polyester polyurethane utilized inthe aqueous dispersions of the present invention have a weight averagemolecular weight from 500 to 3000, such as 500 to 2500, or, in somecases, 900 to about 1300.

In certain embodiments, the amount of polyester polyol used to preparethe polymerizable polyester polyurethane included in certain embodimentsof the present invention ranges from 10 to 60 percent by weight, such as20 to 50 percent by weight or, in some cases, 30 to 40 percent byweight, with the weight percents being based on the total weight ofresin solids used to prepare the polymerizable polyester polyurethane.

As indicated, the polymerizable polyester polyurethane present incertain embodiments of the aqueous dispersions of the present inventionis formed from a material comprising an ethylenically unsaturated groupand an active hydrogen group. Suitable ethylenically unsaturated groupsinclude, for example, acrylates, methacrylates, allyl carbamates, andallyl carbonates. The acrylate and methacrylate functional groups may berepresented by the formula, CH₂═C(R₁)—C(O)O—, wherein R₁ is hydrogen ormethyl. The allyl carbamates and carbonates may be represented by theformulae, CH₂═CH—CH₂—NH—C(O)O—, and CH₂═CH—CH₂—O—(O)O—, respectively.

In certain embodiments, the material comprising an ethylenicallyunsaturated group and an active hydrogen group utilized in preparing thepolymerizable polyester polyurethane comprises ahydroxyalkyl(meth)acrylate. Suitable hydroxyalkyl (meth)acrylatesinclude those having from 1 to 18 carbon atoms in the alkyl radical, thealkyl radical being substituted or unsubstituted. Specific non-limitingexamples of such materials include 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate,hexane-1,6-diol mono(meth)acrylate, 4-hydroxybutyl (meth)acrylate, aswell as mixtures thereof. As used herein, the term “(meth)acrylate” ismeant to include both acrylates and methacrylates.

In certain embodiments, the amount of the material comprising anethylenically unsaturated group and an active hydrogen group used toprepare the polymerizable polyester polyurethane ranges from 1 to 12percent by weight, such as 2 to 8 percent by weight or, in some cases, 4to 6 percent by weight, with the weight percents being based on thetotal weight of resin solids used to prepare the polymerizable polyesterpolyurethane.

As previously indicated, in certain embodiments, the polymerizablepolyester polyurethane present in certain embodiments of the aqueousdispersions of the present invention is formed from a polyamine. Usefulpolyamines include, but are not limited to, primary or secondarydiamines or polyamines in which the groups attached to the nitrogenatoms can be saturated or unsaturated, aliphatic, alicyclic, aromatic,aromatic-substituted-aliphatic, aliphatic-substituted-aromatic andheterocyclic. Exemplary suitable aliphatic and alicyclic diaminesinclude 1,2-ethylene diamine, 1,2-porphylene diamine, 1,8-octanediamine, isophorone diamine, propane-2,2-cyclohexyl amine, and the like.Exemplary suitable aromatic diamines include phenylene diamines and thetoluene diamines, for example, o-phenylene diamine and p-tolylenediamine. These and other suitable polyamines are described in detail inU.S. Pat. No. 4,046,729 at column 6, line 61 to column 7, line 26, thecited portion of which being incorporated herein by reference.

In certain embodiments, the amount of polyamine used to prepare thepolymerizable polyester polyurethane ranges from 0.5 to 5 percent byweight, such as 1 to 4 percent by weight or, in some cases, 2 to 3percent by weight, with the weight percents being based on the totalweight of resin solids used to prepare the polymerizable polyesterpolyurethane.

As previously indicated, in certain embodiments, the polymerizablepolyester polyurethane present in certain embodiments of the aqueousdispersions of the present invention is formed from a materialcomprising an acid functional group or anhydride and a functional groupreactive with the isocyanate or hydroxyl groups of other components fromwhich the polyurethane material is formed. Useful acid functionalmaterials include compounds having the structure:X-Y-Zwherein X is OH, SH, NH₂, or NHR, and R includes alkyl, aryl,cycloalkyl, substituted alkyl, substituted aryl, and substitutedcycloalkyl groups, and mixtures thereof; Y includes alkyl, aryl,cycloalkyl, substituted alkyl, substituted aryl, and substitutedcycloalkyl groups, and mixtures thereof; and Z includes OSO₃H, COOH,OPO₃H₂, SO₂OH, POOH, and PO₃H₂, and mixtures thereof.

Examples of suitable acid functional materials include hydroxypivalicacid, 3-hydroxy butyric acid, D,L-tropic acid, D,L hydroxy malonic acid,D,L-malic acid, citric acid, thioglycolic acid, glycolic acid, aminoacid, 12-hydroxy stearic acid, dimethylol propionic acid, mercaptopropionic acid, mercapto butyric acid, mercapto-succinic acid, andmixtures thereof.

Useful anhydrides include aliphatic, cycloaliphatic, olefinic,cycloolefinic and aromatic anhydrides. Substituted aliphatic andaromatic anhydrides also are useful provided the substituents do notadversely affect the reactivity of the anhydride or the properties ofthe resultant polyurethane. Examples of substituents include chloro,alkyl and alkoxy. Examples of anhydrides include succinic anhydride,methylsuccinic anhydride, dodecenyl succinic anhydride,octadecenylsuccinic anhydride, phthalic anhydride, tetrahydrophthalicanhydride, methyltetrahydrophthalic anhydride, hexahydrophthalicanhydride, alkyl hexahydrophthalic anhydrides such asmethylhexahydrophthalic anhydride, tetrachlorophthalic anhydride,endomethylene tetrahydrophthalic anhydride, trimellitic anhydride,chlorendic anhydride, itaconic anhydride, citraconic anhydride, maleicanhydride, and mixtures thereof.

In certain embodiments, the acid functional material or anhydrideprovides the polymerizable polyester polyurethane with anionic ionizablegroups which can be ionized for solubilizing the polymer in water. As aresult, in certain embodiments, the polymerizable polyester polyurethanepresent in certain embodiments of the aqueous dispersions of the presentinvention is water-dispersible. As used herein, the term“water-dispersible” means that a material may be dispersed in waterwithout the aid or use of a surfactant. As used herein, the term“ionizable” means a group capable of becoming ionic, i.e., capable ofdissociating into ions or becoming electrically charged. An acid may beneutralized with base to from a carboxylate salt group. Examples ofanionic groups include —OSO₃ ⁻, —COO⁻, —OPO₃ ⁼, —SO₂O, —POO⁻; and PO₃ ⁼.

In certain embodiments, the amount of the material comprising an acidfunctional group or anhydride and a functional group reactive withisocyanate or hydroxyl groups used to prepare the polymerizablepolyester polyurethane ranges from 5 to 20 percent by weight, such as 7to 15 percent by weight or, in some cases, 8 to 12 percent by weight,with the weight percents being based on the total weight of resin solidsused to prepare the polymerizable polyester polyurethane.

As indicated, in certain embodiments, the acid groups are neutralizedwith a base. Neutralization can range from about 0.6 to about 1.1, suchas 0.4 to 0.9 or, in some cases, 0.8 to 1.0, of the total theoreticalneutralization equivalent. Suitable neutralizing agents includeinorganic and organic bases such as sodium hydroxide, potassiumhydroxide, ammonia, amines, alcohol amines having at least one primary,secondary, or tertiary amino group and at least one hydroxyl group.Suitable amines include alkanolamines such as monoethanolamine,diethanolamine, dimethylaminoethanol, diisopropanolamine, and the like.

The polymerizable polyester polyurethane utilized in certain embodimentsof the aqueous dispersions of the present invention may be formed bycombining the above-identified components in any suitable arrangement.For example, the polymerizable polyester polyurethane may be prepared bysolution polymerization techniques understood by those skilled in theart to which the present invention pertains.

As should be apparent from the foregoing description, the polymerizablepolyester polyurethane present in certain embodiments of the presentinvention can be nonionic, anionic or cationic. In certain embodiments,the polymerizable polyester polyurethane will have a weight averagemolecular weight of less than 150,000 grams per mole, such as from10,000 to 100,000 grams per mole, or, in some cases, from 40,000 to80,000 grams per mole. The molecular weight of the polyurethane andother polymeric materials used in the practice of the invention isdetermined by gel permeation chromatography using a polystyrenestandard.

As should be apparent from the foregoing description, the presentinvention is also directed to water-dispersible, polymerizable polyesterpolyurethanes comprising terminal ethylenically unsaturated groups andformed from components comprising (a) a polyisocyanate, (b) a polyesterpolyol, (c) a polyamine, (d) a material having an ethylenicallyunsaturated group and an active hydrogen group, and (e) a materialhaving an acid functional group or anhydride and an active hydrogengroup. In certain embodiments, the present invention is directed towater-dispersible, polymerizable polyester polyurethanes comprisingterminal ethylenically unsaturated groups formed from componentscomprising (a) a polyisocyanate present in an amount ranging from 20 to70 weight percent, (b) a polyester polyol present in an amount rangingfrom 10 to 60 weight percent, (c) a polyamine present in an amountranging from 0.5 to 5 weight percent, (d) a material having anethylenically unsaturated group and an active hydrogen group present inan amount ranging from 1 to 12 weight percent, and (e) a material havingan acid functional group or anhydride and an active hydrogen grouppresent in an amount ranging from 5 to 20 weight percent.

As previously indicated, in certain embodiments of the aqueousdispersions of the present invention, a friable polymer is present thatcomprises the reaction product of (i) a polymerizable polyesterpolyurethane, such as that previously described, and (ii) anethylenically unsaturated monomer. Suitable ethylenically unsaturatedmonomers include any of the polymerizable ethylenically, unsaturatedmonomers, including vinyl monomers known in the art. Non-limitingexamples of useful ethylenically unsaturated carboxylic acid functionalgroup-containing monomers include (meth)acrylic acid, beta-carboxyethylacrylate, acryloxypropionic acid, crotonic acid, fumaric acid, monoalkylesters of fumaric acid, maleic acid, monoalkyl esters of maleic acid,itaconic acid, monoalkyl esters of itaconic acid and mixtures thereof.As used herein, “(meth)acrylic” and terms derived therefrom are intendedto include both acrylic and methacrylic.

Non-limiting examples of other useful ethylenically unsaturated monomersfree of carboxylic acid functional groups include alkyl esters of(meth)acrylic acids, for example, ethyl(meth)acrylate,methyl(meth)acrylate, butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,2-hydroxyethyl(meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl(meth)acrylate, isobornyl(meth)acrylate, lauryl (meth)acrylate, andethylene glycol di(meth)acrylate; vinyl aromatics such as styrene andvinyl toluene; (meth)acrylamides such as N-butoxymethyl acrylamide;acrylonitriles; dialkyl esters of maleic and fumaric acids; vinyl andvinylidene halides; vinyl acetate; vinyl ethers; allyl ethers; allylalcohols; derivatives thereof and mixtures thereof.

The ethylenically unsaturated monomers also can include ethylenicallyunsaturated, beta-hydroxy ester functional monomers, such as thosederived from the reaction of an ethylenically unsaturated acidfunctional monomer, such as a monocarboxylic acid, for example, acrylicacid, and an epoxy compound which does not participate. in the freeradical initiated polymerization with the unsaturated acid monomer.Examples of such epoxy compounds are glycidyl ethers and esters.Suitable glycidyl ethers include glycidyl ethers of alcohols and phenolssuch as butyl glycidyl ether, octyl glycidyl ether, phenyl glycidylether and the like.

In certain embodiments, the polymerizable polyester polyurethane and theethylenically unsaturated monomer are present in the aqueous dispersionsof the present invention in a weight ratio of 95:5 to 30:70, such as90:10 to 40:60, or, in some cases, from 80:20 to 60:40.

The aqueous dispersions comprising polymer-enclosed particles of thepresent invention, whether they include a friable polymer or not, can beprepared by any of a variety of methods. For example, in certainembodiments, the aqueous dispersions of the present invention areprepared by a method comprising (A) providing a mixture, in an aqueousmedium, of (i) particles, (ii) one or more polymerizable, ethylenicallyunsaturated monomers; and/or (iii) a mixture of one or morepolymerizable unsaturated monomers with one or more polymers; and/or(iv) one or more polymers, and then subjecting the mixture to highstress shear conditions in the presence of an aqueous medium.

Such methods are described in detail in U.S. patent application Ser. No.10/876,031 at [0054] to [0090], incorporated by reference herein, andUnited States Published Patent Application 2005/0287348 at [0036] to[0050], the cited portion of which being incorporated herein byreference.

In other embodiments, however, the aqueous dispersions of the presentinvention are made by a method comprising (1) providing a mixture, in anaqueous medium, of (i) particles, (ii) a polymerizable ethylenicallyunsaturated monomer, and (iii) a water-dispersible polymerizabledispersant, and (2) polymerizing the ethylenically unsaturated monomerand polymerizable dispersant to form polymer-enclosed particlescomprising a water-dispersible polymer. In these embodiments, thepolymerizable dispersant may comprise any polymerizable material that iswater-dispersible and which, upon polymerization with the ethylenicallyunsaturated monomer, produces polymer-enclosed particles comprising awater-dispersible polymer, in some cases, a water-dispersible, friablepolymer. In certain embodiments, the polymerizable dispersant comprisesthe previously described water-dispersible, polymerizable polyesterpolyurethane having terminal ethylenic unsaturation.

In these embodiments, the water-dispersible polymerizable dispersant iscapable is dispersing itself and other materials, including theethylenically unsaturated monomers, in the aqueous medium without theneed for surfactants and/or high shear conditions. As a result, theforegoing method for making an aqueous dispersion of polymer-enclosedparticles is particularly suitable in situations where use of the highstress shear conditions described U.S. patent application Ser. No.10/876,031 at [0081] to [0084] and United States Published PatentApplication No. 2005/0287348 at [0046], is not desired or feasible.Therefore, in certain embodiments, the aqueous dispersions of thepresent invention are prepared by a method that does not include thestep of subjecting the mixture of particles, polymerizable ethylenicallyunsaturated monomer, and water-dispersible polymerizable dispersant tohigh stress shear conditions.

In addition, the foregoing method of the present invention enables theformation of nanoparticles in situ, rather than requiring the formationof nanoparticles prior preparation of the aqueous dispersion. In thesemethods, particles having an average particle size of 1 micron or more,after being mixed with the ethylenically unsaturated monomer and thewater-dispersible polymerizable dispersant in the aqueous medium, may beformed into nanoparticles (i.e., the nanoparticles are formed in situ).In certain embodiments, the nanoparticles are formed by subjecting theaqueous medium to pulverizing conditions. For example, the particles canbe milled with milling media having a particle size of less than 0.5millimeters, or less than 0.3 millimeters, or, in some cases, less than0.1 millimeters. In these embodiments, the particles can be milled tonanoparticle size in a high energy mill in the presence of the aqueousmedium, the polymerizable ethylenically unsaturated monomer, and thewater-dispersible polymerizable dispersant. If desired, anotherdispersant can be used, such as SOLSPERSE 27000, available from Avecia,Inc.

As indicated, the foregoing methods for making aqueous dispersions ofthe present invention include the step of free-radically polymerizingthe ethylenically unsaturated monomer and polymerizable dispersant toform polymer-enclosed particles comprising a water-dispersible polymer.In certain embodiments, at least a portion of the polymerization occursduring formation of nanoparticles, if applicable. Also, a free radicalinitiator may be used. Both water and oil soluble initiators can beused.

Non-limiting examples suitable water-soluble initiators include ammoniumperoxydisulfate, potassium peroxydisulfate and hydrogen peroxide.Non-limiting examples of oil soluble initiators include t-butylhydroperoxide, dilauryl peroxide and 2,2′-azobis(isobutyronitrile). Inmany cases, the reaction is carried out at a temperature ranging from20° to 80° C. The polymerization can be carried out in either a batch ora continuous process. The length of time necessary to carry out thepolymerization can range from, for example, 10 minutes to 6 hours,provided that the time is sufficient to form a polymer in situ from theone or more ethylenically unsaturated monomers.

Once the polymerization process is complete, the resultant product is astable dispersion of polymer-enclosed particles in an aqueous mediumwhich can contain some organic solvent. Some or all of the organicsolvent can be removed via reduced pressure distillation at atemperature, for example, of less than 40° C. As used herein, the term“stable dispersion” or “stably dispersed” means that thepolymer-enclosed particles neither settle nor coagulate nor flocculatefrom the aqueous medium upon standing.

In certain embodiments, the polymer-enclosed particles are present inthe aqueous dispersions of the present invention in an amount of atleast 10 weight percent, or in an amount of 10 to 80 weight percent, orin an amount of 25 to 50 weight percent, or in an amount of 25 to 40weight percent, with weight percents being based on weight of totalsolids present in the dispersion.

In certain embodiments, the dispersed polymer-enclosed particles have amaximum haze of 10%, or, in some cases, a maximum haze of 5%, or, in yetother cases, a maximum haze of 1%, or, in other embodiments, a maximumhaze of 0.5%. As used herein, “haze” is determined by ASTM D1003.

The haze values for the polymer-enclosed particles described herein aredetermined by first having the particles, such as nanoparticles,dispersed in a liquid (such as water, organic solvent, and/or adispersant, as described herein) and then measuring these dispersionsdiluted in a solvent, for example, butyl acetate, using a Byk-GardnerTCS (The Color Sphere) instrument having a 500 micron cell path length.Because the % haze of a liquid sample is concentration dependent, the %haze as used herein is reported at a transmittance of about 15% to about20% at the wavelength of maximum absorbance. An acceptable haze may beachieved for relatively large particles when the difference inrefractive index between the particles and the surrounding medium islow. Conversely, for smaller particles, greater refractive indexdifferences between the particle and the surrounding medium may providean acceptable haze.

In the foregoing methods of the present invention, upon reaction of theethylenically unsaturated monomer with the polymerizable dispersant,polymer-enclosed particles are formed, which, as previously indicated,the inventors believe results in a phase barrier that physicallyprevents the particles, particularly nanoparticles, fromre-agglomerating within the aqueous dispersion. As a result, theforegoing methods of the present invention result in an aqueousdispersion of particles, such as nanoparticles, wherein reagglomerationof the nanoparticles is minimized or avoided altogether.

In certain embodiments, the present invention is directed to methods formaking polymer-enclosed particles. These methods comprise the methodsfor making an aqueous dispersion of polymer-enclosed particles, aspreviously described, wherein the polymer-enclosed particles comprise afriable polymer and further comprising (1) removing water from theaqueous dispersion to form a solid material comprising thepolymer-enclosed particles, and (2) fragmenting the solid material. Inthese embodiments, the water can be removed from the aqueous dispersionby any suitable drying method, such as through the use of a drum dryer,a roller dryer, a spray dryer, or the like. Moreover, the solid materialcan be fragmented by any suitable technique, such as through the use ofa hammer mill or the like. Following fragmentation, the resultantgranules may be further processed, such as by being screened in aclassifier, before packaging.

The present invention is also directed to powder coating compositionsformed from an aqueous dispersion of polymer-enclosed particles. As usedherein, the term “powder coating composition” refers to compositionssuitable for producing a coating, which are embodied in solidparticulate form, rather than liquid form. In certain embodiments of thepowder coating compositions of the present invention, thepolymer-enclosed particles comprise nanoparticles.

In addition to the polymer-enclosed particles, the powder coatingcompositions of the present invention may comprise a particulatefilm-forming resin. Suitable film-forming resins include, for example,an epoxy resin, such as an epoxy group-containing acrylic polymer or apolyglycidyl ether of a polyhydric alcohol and a suitable curing agentfor the epoxy resin, such as a polyfunctional carboxylic acidgroup-containing material or a dicyanamide. Examples of curableparticulate resinous materials are described in Reissue U.S. Pat. No. RE32,261 and U.S. Pat. No. 4,804,581, incorporated by reference herein.Examples of other suitable particulate film-forming resins arecarboxylic acid functional resins, such as carboxylic acid functionalpolyesters and acrylic polymers and suitable curing agents for suchmaterials, such as triglycidyl isocyanurate and beta-hydroxyalkylamidecuring agents as described, for example, in U.S. Pat. No. 4,801,680 andU.S. Pat. No. 4,988,767, incorporated by reference herein.

In certain embodiments, the powder coating compositions of the presentinvention contain from 50 to 90 percent by weight, such as 60 to 80percent by weight, of the particulate film-forming resin, based on thetotal weight of the powder coating composition. In certain embodiments,the powder coating compositions of the present invention contain from0.1 to 50 percent by weight, such as 1 to 20 percent by weight, ofpolymer-enclosed particles, based on the total weight of the powdercoating composition.

The powder coating compositions of the present invention can optionallyinclude other materials such as other pigments, fillers, lightstabilizers, flow modifiers, anti-popping agents, and anti-oxidants.Suitable pigments include, for example, titanium dioxide, ultramarineblue, phthalocyanine blue, phthalocyanine green, carbon black, graphitefibrils, black iron oxide, chromium green oxide, ferride yellow andquindo red.

Anti-popping agents can be added to the composition to allow anyvolatile material to escape from the film during baking. Benzoin is acommonly preferred anti-popping agent and when used is generally presentin amounts of from 0.5 to 3.0 percent by weight based on total weight ofthe powder coating composition.

In certain embodiments, the powder coating compositions of the presentinvention include fumed silica or the like to reduce caking of thepowder during storage. An example of a fumed silica is sold by CabotCorporation under the trademark CAB-O-SIL. The fumed silica is presentin amounts ranging from 0.1 to 1 percent by weight based on total weightof the powder coating formulation.

The present invention is also directed to methods for making powdercoating compositions. In certain embodiments, wherein thepolymer-enclosed particles comprise a friable polymer, thepolymer-enclosed particles and other coating components are all embodiedin a dried, particulate form, blended together, and then melt blended inan extruder. In other embodiments, however, such as those cases whereinan aqueous dispersion of polymer-enclosed particles is used that doesnot include a friable polymer, the powder coating compositions of thepresent invention are made by a method comprising (1) introducing to anextruder powder coating composition components comprising: (a) anaqueous dispersion of polymer-enclosed particles, and (b) dry materials;(2) blending (a) and (b) in the extruder; (3) devolatilizing the blendto form an extrudate; (4) cooling the extrudate, and (5) milling theextrudate to a desired particle size. As used herein, the term“devolatize” means to remove volatile materials, including water andorganic solvents. In certain embodiments, such powder coatingcompositions are made by a method and/or apparatus described in UnitedStates Patent Application Publication Nos. 2005/0212159A1;2005/0213423A1; and/or 2005/0212171A1, the relevant disclosures of whichbeing incorporated herein by reference.

In yet other embodiments, such powder coating compositions are made by amethod that comprises (a) introducing an aqueous dispersion ofpolymer-enclosed particles to a mixture comprising dry materials andwater, and (b) removing the water from the resulting mixture. In theseembodiments, the water can be removed by any suitable drying method,such as through the use of a drum dryer, a roller dryer, a spray dryer,or the like. Moreover, the solid material can be further processed, suchas by fragmenting by any suitable technique, such as through the use ofa hammer mill or the like. The solid material may also be processedthrough an extruder and/or screened in a classifier, before packaging.

In these methods of the present invention, the dry materials may includethe particulate film-forming resin described earlier as well as anyother composition additives. The dry materials may be first blending ina high shear mixer such as a planetary mixture. In certain embodiments,the dry materials and the aqueous dispersion of the present inventionare then blended in an extruder at a temperature ranging from 80° C. to150° C. The extrudate is then cooled and pulverized into a particulateblend.

The powder coating compositions of the invention can be applied to avariety of substrates including metallic substrates, for example,aluminum and steel substrates. The powder coating compositions are oftenapplied by spraying, and in the case of a metal substrate, byelectrostatic spraying, or by the use of a fluidized bed. The powdercoating compositions of the present invention can be applied in a singlesweep or in several passes to provide a film having a thickness aftercure of from about 1 to 10 mils (25 to 250 micrometers), usually about 2to 4 mils (50 to 100 micrometers). In many cases, after application ofthe powder coating composition, the coated substrate is heated to atemperature sufficient to cure the coating, often to a temperatureranging from 250° F. to 500° F. (121.1° C. to 260.0° C.) for 1 to 60minutes, such as 300° F. to 400° F. (148.9° C. to 204.4° C.) for 15 to30 minutes.

As a result, the present invention is also directed to substrates, suchas metal substrates, at least partially coated by a coating depositedfrom a powder coating composition of the present invention.

The powder coating compositions of the present invention may be used toform a single coating, for example, a monocoat, a clear top coating or abase coat in a two-layered system or both; or as one or more layers of amulti-layered system including a clear top coating composition, acolorant layer and/or a base coating composition, and/or a primer layer,including, for example, an electrodeposition primer and/or aprimer-surfacer layer.

The present invention is also directed to substrates at least partiallycoated with a multi-layer composite coating wherein at least one coatinglayer is deposited from such a composition. In certain embodiments, forexample, the powder coating composition of the present inventioncomprises the basecoat layer in a multi-layer composite coatingcomprising a basecoat and a topcoat. As a result, in these embodiments,after application and curing of the powder coating composition of thepresent invention, at least one topcoat layer can be applied to thebasecoat layer. The topcoat can, for example, be deposited from a powdercoating composition, an organic solvent-based coating composition or awater-based coating composition, as is well known in the art. Thefilm-forming composition of the topcoat can be any of the compositionsuseful in coatings applications, including, for example, a film-formingcomposition that comprises a resinous binder selected from acrylicpolymers, polyesters, including alkyds, and polyurethanes. The topcoatcomposition can be applied by any conventional coating technique such asbrushing, spraying, dipping or flowing, but they are most often appliedby spraying. The usual spray techniques and equipment for air spraying,airless spray and electrostatic spraying in either manual or automaticmethods can be used.

In certain embodiments, the present invention is directed to reflectivesurfaces at least partially coated with a color-imparting non-hidingcoating layer deposited from a powder coating composition comprising aplurality of polymer-enclosed nanoparticles having a maximum haze of10%. In certain embodiments, a clearcoat layer may be deposited over atleast a portion of the color-imparting non-hiding coating layer.

As used herein, the term “reflective surface” refers to a surfacecomprising a reflective material having a total reflectance of at least30%, such as at least 40%. “Total reflectance” refers herein to theratio of reflected light from an object relative to the incident lightthat impinges on the object in the visible spectrum integrating over allviewing angles. “Visible spectrum” refers herein to that portion of theelectromagnetic spectrum between wavelengths 400 and 700 nanometers.“Viewing angle” refers herein to the angle between the viewing ray and anormal to the surface at the point of incidence. The reflectance valuesdescribed herein may be determined, for example, by using a MinoltaSpectrophotometer CM-3600d according to the manufacturer suppliedinstructions.

In certain embodiments, the reflective surface comprises a substratematerial such as, for example, polished aluminum, cold roll steel,chrome-plated metal, or vacuum deposited metal on plastic, among others.In other embodiments, the reflective surface may comprise a previouslycoated surface which may, for example, comprise a reflective coatinglayer deposited from a coating composition, such as, for example, asilver metallic basecoat layer, a colored metallic basecoat layer, amica containing basecoat layer, or a white basecoat layer, among others.

Such reflective coating layers may be deposited from a film-formingcomposition that may, for example, include any of the film-formingresins typically used in protective coating compositions. For example,the film-forming composition of the reflective coating may comprise aresinous binder and one or more pigments to act as the colorant. Usefulresinous binders include, but are not limited to, acrylic polymers,polyesters, including alkyds and polyurethanes. The resinous binders forthe reflective coating composition may, for example, be embodied in apowder coating composition, an organic solvent-based coating compositionor a water-based coating composition.

As noted, the reflective coating composition can contain pigments ascolorants. Suitable pigments for the reflective coating compositioninclude, for example, metallic pigments, which include aluminum flake,copper or bronze flake and metal oxide coated mica; non-metallic colorpigments, such as titanium dioxide, iron oxide, chromium oxide, leadchromate, and carbon black; as well as organic pigments, such as, forexample, phthalocyanine blue and phthalocyanine green.

The reflective coating composition can be applied to a substrate by anyconventional coating technique such as brushing, spraying, dipping orflowing, among others. The usual spray techniques and equipment for airspraying, airless spraying and electrostatic spraying in either manualor automatic methods can be used. During application of the basecoat tothe substrate, the film thickness of the basecoat formed on thesubstrate often ranges from 0.1 to 5 mils (2.5 to 127 micrometers), or0.1 to 2 mils (2.5 to 50.8 micrometers).

After forming a film of the reflective coating on the substrate, thereflective coating can be cured or alternatively given a drying step inwhich solvent is driven out of the basecoat film by heating or an airdrying period before application of subsequent coating compositions.Suitable drying conditions will depend on the particular basecoatcomposition, and one the ambient humidity if the composition iswater-borne, but often, a drying time of from 1 to 15 minutes at atemperature of 75° to 200° F. (21° to 93° C.) will be adequate.

The reflective surfaces of the present invention are at least partiallycoated with a color-imparting non-hiding coating layer deposited from apowder coating composition of the present invention. As used herein, theterm “non-hiding coating layer” refers to a coating layer wherein, whendeposited onto a surface, the surface beneath the coating layer isvisible. In certain embodiments of the present invention, the surfacebeneath the non-hiding coating layer is visible when the non-hidinglayer is applied at a dry film thickness of 0.5 to 5.0 mils (12.7 to 127microns). One way to assess non-hiding is by measurement of opacity. Asused herein, “opacity” refers to the degree to which a material obscuresa substrate.

“Percent opacity” refers herein to the ratio of the reflectance of a drycoating film over a black substrate of 5% or less reflectance, to thereflectance of the same coating film, equivalently applied and dried,over a substrate of 85% reflectance. The percent opacity of a drycoating film will depend on the dry film thickness of the coating andthe concentration of color-imparting particles. In certain embodimentsof the present invention, the color-imparting non-hiding coating layerhas a percent opacity of no more than 90 percent, such as no more than50 percent, at a dry film thickness of one (1) mil (about 25 microns).

In certain embodiments of the reflective surfaces of the presentinvention, a clearcoat layer is deposited over at least a portion of thecolor-imparting non-hiding coating layer. The clearcoat layer may bedeposited from a composition that comprises any typically film-formingresin and can be applied over the color-imparting non-hiding layer toimpart additional depth and/or protective properties to the surfaceunderneath. The resinous binders for the clearcoat can be embodied as apowder coating composition, an organic solvent-based coatingcomposition, or a water-based coating composition. Optional ingredientssuitable for inclusion in the clearcoat composition include those whichare well known in the art of formulating surface coatings, such as thosematerials described earlier. The clearcoat composition can be applied toa substrate by any conventional coating technique such as brushing,spraying, dipping or flowing, among others.

In certain embodiments, coatings deposited from a powder coatingcomposition of the present invention exhibit a “richer” color ascompared to a similar powder coating composition that does not include aplurality of polymer-enclosed nanoparticles having a maximum haze of10%, such as those described above. As a result, the present inventionis directed to methods for increasing the color richness of a coatingdeposited from a powder coating composition. These methods compriseincluding in the powder coating composition a plurality ofpolymer-enclosed nanoparticles having a maximum haze of 10%. As usedherein, the term “color richness” refers to the L* value in the CIELABcolor system as described in U.S. Pat. No. 5,792,559 at col. 1, lines 34to 64, the cited portion of which being incorporated herein byreference, wherein a lower L* value corresponds to a higher level ofcolor richness. For purposes of the present invention, colormeasurements at various angles can be made using an X-RITEspectrophotometer, such as an MA68I Multi-angle spectrophotometer,commercially available from X-Rite Instruments, Inc.

The present invention is also directed to methods for matching the colorof a preselected protective and decorative coating deposited from aliquid coating composition. The inventors have discovered that, unlikeprior art powder coating compositions, the powder coating compositionsof the present invention are capable of producing coatings that exhibitcolor properties similar to coatings deposited from liquid coatingcompositions. As a result, the powder coating compositions of thepresent invention can be used for color matching of coatings depositedfrom liquid coating compositions. These methods comprise: (a)determining the visible color of the preselected coating by measuringthe absorbance or reflectance of the preselected coating; and (b) makinga powder coating composition comprising a plurality of polymer-enclosednanoparticles having a maximum haze of 10%, wherein a coating depositedfrom the powder coating composition matches the visible color of thepreselected coating. In these methods, the absorbance or reflectance ofthe preselected coating is determined using a spectrophotometer (asdescribed above) and a curve of the absorbance or reflectance across therange of wavelengths corresponding to the visible spectrum is produced.This curve is referred to as the visible absorbance or reflectancespectrum. A powder coating composition is produced, which includes aplurality of polymer-enclosed nanoparticles having a maximum haze of10%, such that the coating deposited from the powder coating compositionhas a visible absorbance or reflectance spectrum closely matching thatof the preselected coating.

The present invention is also directed to surfaces, such as a reflectivesurface, at least partially coated with a transparent tinted coatingexhibiting a plurality of hues, wherein the transparent tinted coatingis deposited from a coating composition, such as a powder coatingcomposition, comprising polymer-enclosed color-imparting particles ofthe type described herein, wherein the coating has a plurality ofthicknesses. As used herein, the term “hue” refers to the quality of acolor as determined by its dominant wavelength. As used herein, the term“plurality” means two or more. As used herein, the term “transparent”,refers to a coating wherein a surface beyond the coating is visible tothe naked eye when viewed through the coating. Depending upon thedesired application, such a transparent coating can have relatively lowtransmission, i.e., a spectral transmission of no more than 50% or, insome cases, no more than 10%, or, in yet other cases, no more than 5%,while, in other cases, the transparent article can have a relativelyhigh transmission, i.e., a spectral transmission of more than 50%, insome cases at least 60%, or, in yet other cases, at least 80%. Theforegoing spectral transmission values being measured at a wavelengthranging from 410 nanometers to 700 nanometers, based upon ASTM StandardNo. D-1003 using a Hunter Lab COLORQUEST® II Sphere spectrophotometerthat is available from Hunter Associates Laboratory, Inc. of Reston, Va.

As indicated, in these embodiments of the present invention, thetransparent coating has a plurality of thicknesses. This can be achievedby any of a variety of methods. For example, in certain embodiments,this is achieved by applying the coating to a transparent articlecomprising a surface that has been roughened or textured, so that thethickness of the coating varies along the roughened or textured surface.Alternatively, this can be achieved during the coating deposition step,by differentially depositing the coating over selected portions of thesurface of the article. This can also be achieved by depositing thecoating onto the article and then removing a portion of the coating atcertain locations, such as in any desired pattern form. As a result,articles with a patterned appearance may be produced, if desired. Incertain embodiments, a clear topcoating is deposited over at least aportion of the transparent tinted coating.

In addition, the present invention is also directed to surfaces, such asa reflective surface, at least partially coated with a multi-layercomposite coating comprising a first transparent tinted coatingexhibiting a first color and a second transparent tinted coatingdeposited over at least a portion of the first transparent tintedcoating and exhibiting a second color different from the first color. Inthese multi-layer composite coatings, the transparent tinted coatingsare deposited from a coating composition, such as a powder coatingcomposition, comprising polymer-enclosed color-imparting particles ofthe type described herein, wherein at least one of the transparenttinted coatings, in some cases at least two of the transparent tintedcoatings, have a plurality of thicknesses. In certain embodiments, suchmulti-layer composite coatings further comprise a clear topcoatingdeposited over at least a portion of the first transparent tintedcoating and/or the second transparent tinted coating.

The present invention have discovered that the transparent tintedcoatings deposited from a coating composition of the present invention,such as the previously described powder coating compositions, arecapable of producing unique, vibrant colored coatings suitable forapplication in various applications, such as automotive bodies,automotive parts, aerospace, consumer electronics, and otherapplications, to achieve appearances heretofore unattainable through theuse of conventional coating compositions, particularly conventionalpowder coating compositions.

Illustrating the invention are the following examples that are not to beconsidered as limiting the invention to their details. All parts andpercentages in the examples, as well as throughout the specification,are by weight unless otherwise indicated.

EXAMPLES Example 1 Polyurethane Dispersion

This example describes the preparation of a polyurethane dispersion thatwas subsequently used to the form the polyurethane/nanopigmentdispersions of Examples 2 to 3. The polyurethane dispersion was preparedfrom the following mixture of ingredients in the ratios indicated:Ingredients Weight (grams) Charge I Poly (neopentylglycol adipate)¹780.0 Dimethylolpropionic acid (DMPA) 280.7 Tri-ethylamine 127.1Butylated hydroxytoluene 2.5 Triphenyl phosphite 2.5 Charge IIHydroxyethyl methacrylate (HEMA) 116.7 Butyl methacrylate 791.2 ChargeIII Methylene bis(4-cyclohexylisocyanate) 1175.1 Charge IV Butylmethacrylate 57.5 Charge V Deionized water 4734.8 Ethylenediamine 49.2Dimethylethanolamine 40.6 Charge VI Butyl methacrylate 50¹Poly (neopentylglycol adipate) having a number average molecular weightof 1000.

The polyurethane dispersion was prepared in a four neck round bottomflask equipped with an electronic temperature probe, mechanical stirrer,condenser, and a heating mantle. Charge I was stirred 5 minutes in theflask at a temperature of 90° C. Charge II was added and the mixture wascooled to 60° C. Charge III was added over a 10 minute period. Charge IVwas added and the resulting mixture was gradually heated to 90° C. over45 minutes and then held at 90° C. for 3 hours. Charge V was stirred ina separate flask and heated to 80° C. 3000.0 g of the reaction productof Charges I, II, III, and IV was added to Charge V over 30 minutes.Charge VI was added and the resulting mixture was cooled to roomtemperature. The final product was a translucent emulsion with an acidvalue of 12.1, a Brookfield viscosity of 872 centipoise (spindle #3 at30 rpm), a pH of 7.75, and a nonvolatile content of 29.4% as measured at 110° C. for one hour.

Example 2 Polyurethane/Nanopigment Dispersion

This example describes the preparation of a nano-sized PB 15:3phthalocyanine blue pigment dispersion. The dispersion was prepared fromthe following mixture of ingredients in the ratios indicated:Ingredients Weight (grams) Charge I Polyurethane dispersion of Example 14772.7 Deionized water 2304.5 Hydroquinone methyl ether (MEHQ) 1.36 PB15:3 pigment² 700.0 Shellsol OMS (Shell Chemical Co.) 86.4 Charge IIDeionized water 71.5 t-Butyl hydroperoxide (70% aqueous solution) 5.8Charge III Deionized water 337.2 Ferrous ammonium sulfate 0.13 Sodiummetabisulfite 8.18²Commercially available from BASF Corp.

The ingredients were mixed using a 4.5 inch Cowles blade attached to anair motor. The mixture was then pre-dispersed Premier Mill PSM-11 basketmill containing 353 mL of 1.2-1.7 mm Zirconox YTZ® milling media for1.25 hours at 1000 fpm for the mix blades and 960 rpm pump speed andthen recycled through an Advantis V15 Drais mill containing 500 mL of0.3 mm Zirconox YTZ® grinding media in a one liter grinding chamber. Themixture was milled at 1400 rpm with a pump setting of 19 rpm for a totaltime of 15 hours. The progress of the milling was monitored by visuallyobserving changes in the transparency of thin films of samples drawndown over black and white Leneta paper. Charge II was added and theresulting mixture was stirred 5 minutes. Charge III was added in twoaliquots over 5 minutes. The final product was a cyan (Blue) liquid witha Brookfield viscosity of 356 centipoise (spindle #3 at 30 rpm), a pH of7.29, and a nonvolatile content of 28.9% as measured at 110° C. for onehour.

Example 3 Polyurethane/Nanopigment Dispersion

This example describes the preparation of a nano-sized PR 122quinacridone magenta pigment dispersion. The dispersion was preparedfrom the following mixture of ingredients in the ratios indicated:Ingredients Weight (grams) Charge I Polyurethane dispersion of Example 14772.7 Deionized water 2304.5 Hydroquinone methyl ether (MEHQ) 1.36 PR122 pigment³ 700.0 Shellsol OMS (Shell Chemical Co.) 86.4 Charge IIDeionized water 71.5 t-Butyl hydroperoxide (70% aqueous solution) 5.8Charge III Deionized water 337.2 Ferrous ammonium sulfate 0.13 Sodiummetabisulfite 8.18³Commercially available from Sun Chemical.

The ingredients were mixed using a 4.5 inch Cowles blade attached to anair motor. The mixture was then pre-dispersed Premier Mill PSM-11 basketmill containing 353 mL of 1.2-1.7 mm Zirconox YTZ® milling media for 1.5hours at 1000 fpm for the mix blades and 960 rpm pump speed and thenrecycled through an Advantis V15 Drais mill containing 500 mL of 0.3 mmZirconox YTZ® grinding media in a one liter grinding chamber. Themixture was milled at 1260 fpm with a pump setting of 19 rpm for a totaltime of 15 hours. The progress of the milling was monitored by visuallyobserving changes in the transparency of thin films of samples drawndown over black and white Leneta paper. Charge II was added and theresulting mixture was stirred 5 minutes. Charge III was added in twoaliquots over 5 minutes. The final product was a magenta liquid with aBrookfield viscosity of 28.1 centipoise (spindle #3 at 30 rpm), a pH of7.61, and a nonvolatile content of 28.2% as measured at 110° C. for onehour.

Example 4 Preparation of Powder Coating Composition Intermediate

This example describes the preparation of a core formula of drymaterials used to make the powder coating compositions of the subsequentExamples. The core formula was prepared from the following ingredientsin the ratios indicated: Component Ingredients Parts by Weight 1 UralacP880 Resin⁴ 81.136 2 Primid XL552⁵ 11.064 3 Resinflow PL 200A⁶ 1 4Benzoin⁷ 0.7 5 Irganox 1076⁸ 1.2 6 Flow Additive 1.3 7 Tinuvin 144⁹ 1 8Tinuvin 900⁹ 2 9 Transparent Zinc Oxide¹⁰ 0.5 10 Aluminum Oxide C¹¹ 0.01⁴Commercially available from DSM Resins.⁵Commercially available from EMS.⁶Commercially available from Estron Chemical.⁷Commercially available from GCA Chemical.⁸Commercially available from Clariant.⁹Commercially available from CIBA.¹⁰Commercially available from Bayer Chemical.¹¹Commercial available from Palmer Supplies.

Components 1 to 9 were premixed in a Henschel Blender for 1 minute at1000 RPM. The mixture was then extruded through a Coperion W&P 30 mmco-rotating twin screw extruder at a 340 RPM screw speed and an averagetorque of 30-40%. The extruder was equipped with a low pressureinjection system and five independently temperature controlled zones, asdescribed in United States Published Patent ions 2005/0213423;2005/0212159A1; and 2005/0212171A1. The five independently temperaturecontrolled zones were controlled at the following temperatures: Zone 1:60° C.; Zone 2: 120° C.; Zone 3: 130° C.; Zone 4: 120° C.; Zone 5: 100°C. The extrudate was cooled and ground in a mechanical milling system toa particle size of about 28 to 30 microns. Oversized particles wereremoved and component 10 was added.

Example 5 Preparation of Powder Coating Compositions

Two powder coating compositions were prepared. The first powder coatingcomposition was prepared from the composition intermediate of Example 4and the Polyurethane/Nanopigment Dispersion of Example 2. The secondpowder coating composition was prepared from the compositionintermediate of Example 4 and a mixture of the Polyurethane/NanopigmentDispersions of Examples 3 and 2 (weight ratio of 95:5). The compositionintermediate from Example 4 and the pigment dispersions were mixed bycreating powder slurries. The slurries were prepared from the followingmixture of ingredients in the ratios indicated: Example 5A Example 5BComponent (grams) (grams) Example 4 266.3 259.6 Deionized Water 721.7713.6 Example 2 — 25.0 Example 3 12.1 1.9

The slurries were prepared in half gallon metal cans equipped with amechanical stirrer. Each of the powder compositions were prepared bydispersing the composition intermediate of Example 4 in water for fiveminutes to create a slurry; the pigment dispersions were then added tothe slurry and mixed for twenty minutes. The slurries were then pouredinto flat baking pans; the slurry depth was between ¼ inch and ½ inch.The baking pans containing the slurries were then placed in a ventilatedhood and allowed to dry for 16 hours.

The dried powders were then removed from the baking pans and extrudedusing an APV MP19PC co-rotating twin screw extruder at a 450 RPM screwspeed and average torque of 50-60%. The four independently controlledzones were controlled at the following temperatures: Zone 1: 60° C.;Zone 2: 120° C.; Zone 3: 130° C.; Zone 4: 100° C. The extrudate wascooled and 0.01% of Aluminum Oxide C was added. The resulting powder wasthen ground in a mechanical milling system to a particle size of about25-30 microns.

Example 6 Preparation of Wheel

The powder coatings from Example 5 were applied to a Toyota Tacomaaluminum wheel (18 inches). The aluminum wheel was purchasedcommercially and was already coated with a standard wheel coating. Thecoating was removed and the bare aluminum was cleaned and polished. Thesides of the wheel were covered with aluminum foil to protect againstoverspray during powder application.

The stripped wheel was preheated to 340° F. for fifteen minutes. Afterheating, the wheel was mounted vertically on a spray rack in aventilated spray booth. The powder coating from Example 5B waselectrostatically sprayed along the outer edge of the wheel face so thata gradient was created where a heavy coating (approximately 2-3 mils)was applied at the edge of the wheel and no coating was applied at thecenter of the wheel. The coated wheel was then baked at 340° F. fortwenty minutes. After the bake was completed, the wheel was allowed tocool at room temperature for ten minutes. The wheel was then verticallymounted on a spray rack in a ventilated spray booth and approximately 2mils of the powder coating from Example 5A was then electrostaticallysprayed over the entire wheel. The coated wheel was then baked at 340°F. for thirty minutes.

After the bake was completed, the wheel was allowed to cool at roomtemperature for 15 minutes. The wheel was then vertically mounted on aspray rack in a ventilated hood and approximately 2 mils of powderclearcoat PCC10103H (commercially available from PPG Industries) wasthen electrostatically sprayed over the entire wheel face. The coatedwheel was then baked at 340° F. for thirty minutes.

The coating on the wheel exhibited a color gradient ranging from violetaround the rim to light blue in the center.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

1. A reflective surface at least partially coated with a transparenttinted coating exhibiting a plurality of hues, wherein the transparenttinted coating is deposited from a coating composition comprisingpolymer-enclosed color-imparting particles, wherein the coating has aplurality of thicknesses.
 2. The reflective surface of claim 1, whereinthe reflective surface is a reflective substrate.
 3. The reflectivesurface of claim 1, wherein the transparent tinted coating is depositedfrom a powder coating composition.
 4. The reflective surface of claim 3,wherein the powder coating composition is formed from an aqueousdispersion comprising polymer-enclosed color-imparting particles,wherein the polymer-enclosed color-imparting particles compriseparticles enclosed by a friable polymer.
 5. The reflective surface ofclaim 4, wherein the color-imparting particles comprise nanoparticles.6. The reflective surface of claim 5, wherein the color-impartingparticles comprise an organic pigment selected from perylenes,quinacridones, phthalocyanines, isoindolines, dioxazines,1,4-diketopyrrolopyrroles, anthrapyrimidines, anthanthrones,flavanthrones, indanthrones, perinones, pyranthrones, thioindigos,4,4′-diamino-1,1′-dianthraquinonyl, azo compounds, substitutedderivatives thereof, and mixtures thereof.
 7. The reflective surface ofclaim 4, wherein the friable polymer comprises the reaction product of(i) a polymerizable polyester polyurethane, and (ii) an ethylenicallyunsaturated monomer.
 8. The reflective surface of claim 7, wherein thepolymerizable polyester polyurethane is water-dispersible.
 9. Thereflective surface of claim 7, wherein the polymerizable polyesterpolyurethane has a weight average molecular weight of 40,000 to 80,000grams per mole.
 10. The reflective surface of claim 4, wherein theaqueous dispersion is prepared by a method comprising: (A) providing amixture, in an aqueous medium, of (i) color-imparting nanoparticles,(ii) one or more polymerizable, ethylenically unsaturated monomers;and/or (iii) a mixture of one or more polymerizable unsaturated monomerswith one or more polymers; and/or (iv) one or more polymers, and thensubjecting the admixture to high stress shear conditions in the presenceof an aqueous medium to particularize the admixture intopolymer-enclosed color-imparting particles; or (B) providing a mixture,in an aqueous medium, of (i) color-imparting particles, (ii) apolymerizable ethylenically unsaturated monomer, and (iii) awater-dispersible polymerizable dispersant; forming the color-impartingparticles into nanoparticles; and polymerizing the ethylenicallyunsaturated monomer and polymerizable dispersant to formpolymer-enclosed color-imparting particles comprising awater-dispersible polymer.
 11. A reflective surface at least partiallycoated with a multi-layer composite coating comprising: (a) a firsttransparent tinted coating exhibiting a first color; and (b) a secondtransparent tinted coating deposited over at least a portion of thefirst transparent tinted coating and exhibiting a second color differentfrom the first color, wherein the first transparent tinted coating andthe second transparent tinted coating are deposited from a coatingcomposition comprising polymer-enclosed color-imparting particles, andwherein at least one of the transparent tinted coatings have a pluralityof thicknesses.
 12. The reflective surface of claim 11, wherein thereflective surface is a reflective substrate.
 13. The reflective surfaceof claim 11, wherein at least one of the first transparent tintedcoating and the second transparent tinted coating is deposited from apowder coating composition.
 14. The reflective surface of claim 13,wherein the powder coating composition is formed from an aqueousdispersion comprising polymer-enclosed color-imparting particles,wherein the polymer-enclosed color-imparting particles compriseparticles enclosed by a friable polymer.
 15. The reflective surface ofclaim 14, wherein the color-imparting particles comprise nanoparticles.16. The reflective surface of claim 15, wherein the color-impartingparticles comprise an organic pigment selected from perylenes,quinacridones, phthalocyanines, isoindolines, dioxazines,1,4-diketopyrrolopyrroles, anthrapyrimidines, anthanthrones,flavanthrones, indanthrones, perinones, pyranthrones, thioindigos,4,4′-diamino-1,1′-dianthraquinonyl, azo compounds, substitutedderivatives thereof, and mixtures thereof.
 17. The reflective surface ofclaim 14, wherein the friable polymer comprises the reaction product of(i) a polymerizable polyester polyurethane, and (ii) an ethylenicallyunsaturated monomer.
 18. The reflective surface of claim 17, wherein thepolymerizable polyester polyurethane is water-dispersible.
 19. Thereflective surface of claim 14, wherein the aqueous dispersion isprepared by a method comprising: (A) providing a mixture, in an aqueousmedium, of (i) color-imparting nanoparticles, (ii) one or morepolymerizable, ethylenically unsaturated monomers; and/or (iii) amixture of one or more polymerizable unsaturated monomers with one ormore polymers; and/or (iv) one or more polymers, and then subjecting theadmixture to high stress shear conditions in the presence of an aqueousmedium to particularize the admixture into polymer-enclosedcolor-imparting particles; or (B) providing a mixture, in an aqueousmedium, of (i) color-imparting particles, (ii) a polymerizableethylenically unsaturated monomer, and (iii) a water-dispersiblepolymerizable dispersant; forming the color-imparting particles intonanoparticles; and polymerizing the ethylenically unsaturated monomerand polymerizable dispersant to form polymer-enclosed color-impartingparticles comprising a water-dispersible polymer.
 20. A method formaking a powder coating composition comprising: (a) introducing anaqueous dispersion of polymer-enclosed particles to a mixture comprisingdry materials and water, (b) removing the water from the product of step(a) to form a solid material; and (c) fragmenting the solid material.